Turtles' road to parenthood is paved with good intentions

Snapping turtle in Britannia that has just dug a nest (hole in background).- Dan Brunton/Postmedia

It was late June, and an Environment Canada scientist was in Algonquin Park, Ontario, looking for snapping turtle eggs as he studied effects of pollution on wildlife.

Snappers come ashore to bury their eggs in shallow holes, often in sand or gravel by a roadside. But the nests this biologist found were different.

They were buried in asphalt, in road patches so fresh the unmistakable smell of oil was everywhere. And there were three nests, indicating three different mother turtles had gone to work in the same spot.

Asphalt contains some of the same oil-based pollutants that Environment Canada was studying. The department took a closer look, and its study is now published in a science journal called the Canadian Field-Naturalist.

Snappers are remarkably un-picky about where they will nest, the paper notes. They will lay eggs in farm fields, sand, clay, piles of wood chips, vegetable gardens, and even beaver lodges.

They have been found laying eggs in compost piles where the intense heat from bacterial action kills not only the eggs but the turtle that lays them.

And now, asphalt. Specifically a type called cold patch , which is used for small repair jobs when it is not practical to bring in equipment to heat regular asphalt.

Cold patch is mixed with a petroleum-based solvent to keep it soft and workable without heating. The solvent can be diesel, gasoline or kerosene, the paper notes, which are all extremely toxic. But it also kept the material soft enough for snappers to dig into it.

The nests were on the sloping side of a road south of Lake Opeongo away from traffic, and biologist Shane de Solla dug some eggs out of one of them. It was easy digging because the asphalt was not compacted. The white eggs, about the size of ping pong balls, were stained and speckled with bits of asphalt and handling them left a sticky, oily layer on the scientist’s gloves.

Back at the Canada Centre for Inland Waters in Burlington, he exposed snapping turtle eggs to asphalt and then analyzed them. They soaked up toxins, in particular a common oil-based type called polyaromatic hydrocarbons (PAHs). They probably did not absorb enough to kill the turtle embryos, but deformity is another risk.

On a return trip to Algonquin a month later, de Solla found one of the remaining nests had been dug up by a predator (likely a fox, skunk or raccoon) and the last one couldn’t be found. Larger animals had walked around and erased all traces of it.

But why choose asphalt in the first place?

Snappers choose warm, sunny spots where the sun’s energy will warm the eggs, the paper says. But while they carefully select a site, they seem to have no sense of whether it is contaminated.

“Incidents of oviposition in asphalt as described here are presumably not common, but turtles frequently use roadsides for oviposition,” the scientists write. (Oviposition means laying eggs.)

They also note that egg-eating animals were able to sniff out some of the eggs even though all the humans could smell was “pungent” fresh pavement.

Snapping turtles are not endangered and are widespread in North America. They are Canada’s largest freshwater turtle, with a carapace (top shell) length of 20 to 36 centimetres and often weighing about 10 kilograms.